display article in page of main category, not in current.

Hi,

I have articles with more than one category. The url always display the main category, but the article is still displaying in current page/category.

For example: I have a article set to category A and B. A is the main category. The current category in frontend is category B.
If i click on "read more" in Category B, the article is still displayed in category B, although the url display category A.

How i get the correct page view for the item?

thanks